In recent years, a capacity of a storage medium, which stores information, becomes remarkably increasing as an amount of data which is processed by a computer becomes increasing. The storage medium such as a hard disk, a magnetic tape and a disk type storage medium like an optical disk are used in many cases. The hard disk out of the storage media is used as a main storage apparatus since the hard disk has an advantage of the high speed property and the random access property for storing and regenerating data.
In contrast, the magnetic tape and the disk type storage medium are used for archive and backup. The magnetic tape is excellent in a point of the low cost and the large storage capacity per unit volume in comparison with the disk type storage medium. However, the magnetic tape is inferior in a point of the random access property and the data holding property in comparison with the disk type storage medium.
For this reason, it is desired to realize a storage medium which has the excellent points of the disk type storage medium and of the magnetic tape and also has the excellent random access property and the excellent data holding property.
As a method to increase a capacity of the storage medium such as the optical disk, Japanese Patent Application Laid-Open No. 2007-4906 (hereinafter, referred to as patent document 1), Japanese Patent Application Laid-Open No. 2007-172728 (hereinafter, referred to as patent document 2) and Japanese Patent Application Laid-Open No. 2006-216156 (hereinafter, referred to as patent document 3) disclose the method to pile a plurality of the optical disks on the optical disk case and to stock a plurality of the optical disks, which are piled, in the optical disk case. The patent document 1 and the patent document 2 disclose the method that one optical disk is selected out of a plurality of the optical disks, which are stocked, to be taken out, and the optical disk, which is taken out, is transported to the data recording and regenerating drive. The invention described in the patent document 3 discloses the method to transport the optical disk, which is taken out in an order of piling, to the data recording and regenerating drive. The patent document 3 discloses also the case of using the spindle which enables the optical disks to be arranged leaving spaces between them and to pile the optical disks. According to the patent document 3, the optical disk has the hole, whose inner diameter is different for each optical disk, at its center. The axis of the spindle has the form of stair which is corresponding to each hole and is fitted with each the hole.